An Electoral Commission spokesperson told the Belfast Telegraph that they were not planning to investigate the donation.

"We are not investigating the donation received by Sinn Fein from Mr Hampton. The donation reported by the party was permissible as the donor was on a UK electoral roll within the five-year period prior to his death," the spokesperson said.

"Political parties must report all donations and loans over £7,500 if accepted by the central party and over £1,500 if accepted by an accounting unit.

"Political parties must only accept donations from permissible donors. It is the responsibility of political parties to check the permissibility of the donations they receive and to ensure they have systems in place to maintain their compliance with the law."

Sinn Fein said last week that the party was in "full compliance" with the commission regarding the donation.

Mr Hampton died at 82 in January 2018, leaving an estate worth £2.6m.

The majority was handed to the executors and trustees of his will - Joe Cahill and Dessie Mackin - for Sinn Fein.

Mairia Cahill

At the time Mr Cahill and Mr Mackin were the party's national treasurers.

Mr Cahill's great-niece, former SDLP councillor Mairia Cahill, said that the circumstances behind the donation were "fascinating".

"It's like something you would read in a novel," she told BBC Radio Ulster's Nolan Show.

"Interestingly this guy who had £2.6m in assets was living at no fixed abode.

"I think this would make a fantastic film, you don't see every day of the week someone who has that amount of assets but generally doesn't live very ostentatiously or in a wealthy manner."

Ms Cahill said that "due diligence" should be done on the money and Sinn Fein should be "transparent" on how the executors of Mr Hampton's will determined he got the money through family.

A Sinn Fein spokesperson had previously said that Mr Hampton came from a wealthy family background.

Former SDLP councillor Ms Cahill noted that Sinn Fein had taken a hard line stance over donations to other political parties in the past.

"It really would behove this party to be extremely transparent about how this man not only came by his money, but came by the decision to then gift it to who he gifted it to," she said.

Ms Cahill said that her uncle Joe had never mentioned the issue to her before he passed away in 2004.

"He was my great-uncle and he had responsibility for finance for a number of different outfits, if I can put it like that. I was very close to him during my life and I would imagine he had quite a lot of eccentric people he knew," she said.

"If someone had come to me in 1997 and said 'look I'm going to leave you a huge amount of money here in my will when I die', I would have thought that person would have been spoken about fondly or with surprise.

"He never said a word so I find that in itself a bit strange, but Joe never spent a penny of anyone else's money, so maybe he just treated it with the confidence it deserved."